Sliced Steak with Roasted Corn Salsa

Name: Sliced Steak with Roasted-Corn Salsa
Ingredients: 3 cups fresh corn (about 3 ears); 4 scallions, white and green parts thinly sliced separately; 2 tablespoons unsalted butter; 2 garlic cloves, minced; 1 1/2 teaspoons kosher salt; 1 1/2 teaspoons ground cumin; 1 teaspoon chili powder; 1/2 teaspoon black pepper; 2 plum tomatoes, finely diced; 1 to 2 fresh jalapeño chiles, finely diced (including seeds); 1 (2-pound) trimmed boneless sirloin steak, about 1 1/2 inches thick; 1/4 cup finely chopped fresh cilantro; Accompaniment: lime wedges